The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
As is widely known, injection molding of thermoplastic and thermoset materials is often used to form a variety of parts having intricate shapes and requiring close dimensional tolerances. Such injection molding may be accomplished using a wide variety of materials, such as thermoset and thermoplastic materials, rubber, or similar materials.
Many conventional injection molding machines employ a stationary plastic extruder operable to pass a material through a series of runners to one or a plurality of mold cavities. These mold cavities are formed between a pair of separable mold dies and are shaped to closely conform to a predetermined shape. A sprue and a plurality of runners are used to channel material to each mold cavity. That is, once the mold dies are closed, the extruder is actuated to inject a “shot” of material (i.e. plastic or rubber) into the sprue, runners, and mold cavities. The runners are often provided with a fan gate portion for introducing the molded material into the mold cavity. After the material has had sufficient time to solidify, the mold dies are separated and the parts ejected therefrom. Generally, when the parts are ejected from the mold dies, the runners (including the fan gate portion) and sprue associated therewith are also ejected coupled with the molded parts. The solidified runner and sprue material must be separated from the molded parts and finally discarded. In some instances, this discarded material may be recycled back into the manufacturing process. However, thermoset materials are not recyclable and often times, customer requirements may otherwise limit the amount of recycled material that may be used. As should be appreciated, when molding small parts with relatively large sprue and runner channels, the amount of discarded material can often exceed the amount of material that is permitted to be recycled. Therefore, this excess material may not be reused. This leads to increased costs associated with wasted material and disposal of the wasted material.
With injection molding, it is often necessary to perform further machining of the formed parts to achieve the desired surface treatments at these gating locations. The removing of the sprue and gated material and machining is typically necessary to achieve the desired final quality. Thus, it is desirable to select a location for the gating to minimize the need for post-molding machining, yet maintain proper material flow. This is particularly necessary in the forming of ring seals and cylindrical sleeves.
One attempt to simplify injection molding of thermoset parts has been the use of “cold runner” systems wherein the runners from the extruder to the mold cavity are maintained below a predetermined temperature. With this system, the thermoset material in the runners is maintained below the curing temperature with only the material in the mold cavity being solidified. Thus, the parts are ejected from the mold cavity with minimal gated material to be removed therefrom. The amount of sprue and gated material to be removed from the finished parts is greatly reduced with this system, however, the necessity for the removal of a small amount of gated material still exists.
Accordingly, there exists a need in the relevant art to provide an injection molding machine that is capable of fully eliminating the gated material from the molded part. Additionally, there exists a need in the relevant art to provide an injection molding machine that is capable of minimizing the need for post-molding machining.